Loggerhead Life History

Development and migration of loggerheads

Loggerhead sea turtles are a highly migratory, long-lived species. It is estimated that loggerheads do not reach sexual maturity until some time between the ages of 10 and 30 (Parham & Zug 1997). The average adult lives to about the age of 26.5 years and measures 87 cm in straight carapace length - loggerheads probably sexually mature at a much greater length than 87 cm because of slower growth rates (Bjorndal et al. 2000).

Loggerhead sea turtles are omnivorous and prefer benthic mollusks, such as whelks and conchs, and arthropods, such as horseshoe crabs, spider crabs, lady crabs, blue crabs, and hermit crabs (Hopkins-Murphy et al. 2003).

We've recently learned more about turtles on their foraging grounds, through satellite tagging programs. You can see up to date locations of these turtles by clicking on the following link www.seaturtle.org/tagging. One theory is that the turtles use an internal magnetic compass to navigate during these migrations (Limpus et al. 1992, Schroeder et al. 2003). They mate offshore between late March and early June, and the males return to the foraging locations.

In the United States , nesting occurs from May to September along the East Coast from Virginia to the Gulf of Mexico, but the majority of nesting occurs on the Atlantic coast of Florida (DeGroot and Shaw 1993). At night, the female crawls on to the beach. Loggerheads are only on land as hatchlings and egg-laying females, and during these times, they use photic cues to orient themselves. Often the nesting female has a low threshold of alarm when crawling up the beach to the nesting site. Even a small disturbance can cause her to abandon nesting for the night and return to the ocean. This non-nesting emergence is commonly called a “false crawl.” However, once the nesting process begins, the female enters a trance-like state and is oblivious to her surroundings. She digs an inverted light bulb-shaped cavity in the sand above the high tide mark with her rear flippers and deposits 100 to 150 pliable, white, and approximately spherical eggs. The eggs have been described as resembling leathery ping-pong balls. After laying her eggs, the female fills the cavity with sand and attempts to camouflage the nest by throwing sand around with her flippers. Most mature females lay two to three clutches per season on average. The clutches are usually laid in two week intervals (Hedges pers. comm.).

U.S. nesting beaches

Tagging studies indicate that turtles return to within 5 km of their first nesting site for the duration of their egg laying days. Bowen's paper proves that females exhibit natal homing through mtDNA and defines the subpopulations, nDNA analysis suggests male mediated gene flow within the entire North Atlantic population. It has also been suggested a female nests on her natal beach - the beach where she hatched. After nesting, the females return to their foraging habitats. Incubation usually lasts 55 to 65 days. Lower incubation temperatures (26-28°C) produce males, while higher incubation temperatures (31-32°C) produce females.

Hatchlings usually emerge at night and immediately crawl to the ocean. On average, the hatchlings are 45 mm long and weigh 20 g. They swim vigorously until they reach the North Atlantic Gyre. Here they associate with floating mats of Sargassum seaweed.

For 6 to 11 years, the juvenile loggerheads continue to associate with these mats, migrate with gyres as far as the Azores, and forage on the ocean's surface. At an average age of 8.2 years juveniles then move to more shallow waters of near shore and estuarine habitats along the U.S. East Coast to further develop (Bjorndal et al., 2000). They carry out benthic foraging from Long Island Sound to the Gulf of Mexico (Butler et al., 1987). Little is know about their development from the juvenile to adult stage (Ernst et al. 1994, National Research Council 1990, Miller 1997).